Recently, in accordance with the development of electronic technology, users could receive three-dimensional (3D) images through head mounted displays (HMDs).
In this case, the user could receive a 3D image for a direction that he/she views depending on movement of his/her head to feel a more realistic 3D image unlike an existing monitor or television (TV).
However, in the case of enlarging or shrinking the 3D image, a disparity between a left-eye image and a right-eye image is excessively increased, such that a cross talk phenomenon occurs, or a disparity between a left-eye image and a right-eye image is decreased, such that an unnatural image is provided to the user.